Starter



S. W. RUSHMORE.

STARTER.

APPLICATION FILED 020.20, 1920.

1,387,559, Patented Aug. 16, 1921.

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U E I nm To Ra U E AN 6 L. E fiz E] wpwwtoz Jkmzee! liffizuflmon type of starter now UNITED STATES PATENT OFFICE.

STARTER.

Specification of Letters Patent.

Application filed December 20, 1920. Serial No. 431,852.

T 0 all 20120722 62? may concern:

Be it known that I, SAMUEL lV. RUSH- MORE, a citizen of the United States. and resident of Plainfield, in the county of Union and State of New Jersey, have invented certain new and useful Improvements in Starters, of which the following is a specification.

My present invention is disclosed as embodied in a starter of the same type as the electric starters now commonly employed on automobiles, and while this is the preferred embodiment, it will be evident that several novel features of the device may be employed in other connections or for other purposes.

Starters of the tyne referred to usually comprise a small electric motor having a pinion on the armature shaft and means for moving the pinion endwise into engagement with gear teeth out on the periphery of the fly wheel of the engine. In the under consideration this pinion is driven through a torque spring.

My present invention relates more particularly to the torque spring in its relation to the other elements of the combination in connection with which it performs its driving and shock-absorbing functions.

According to present practice. such springs usually have their convolutions formed from material of uniform crosssection. Hence the cross section actually selected is a compromise between the great stiffness which would be desirable to Withstand unusual shocks and the flexibility Which is desirable for purposes of yield under stress, particularly the stresses which are applied when the pinion teeth happen to strike end-on. instead of sliding smoothly into mesh with the teeth of the gear which is to be driven thereby. In practice this attempt to compromise conflicting requirements sometimes results in a spring stiffer than it should be for purposes of engaging the gear and taking up the shock of starting; and even more often, it results in a spring which is so flexible that under; not unusual conditions of high resistance in the engine or high speed of the starting motor, the spring may become completely wound up so that it no longer affords the desired spring resilience. This results in dangerous shock or stress on all operating that the free portions parts of the device and frequently results in breakage of the spring itself.

y my invention I provide shock-absorbing spring which flexible as desired while the pinion is meshing with the ear, yet. after it is in mesh, will become as stiff as desired under maximum torque operating agalnst maximum load. Although this may be worked out in a variety of ways, the preferred way is to make one part of the spring flexible and the other part stiff, and to arrange matters so that as soon as the load ecomes appreciable the flexible part of the spring will wind up and go out of business, leaving the stiffer )arts in full normal rcsilient operation. referably the stiff and flexible portions of the spring merge gradually one into the other, and preferably the stiff portion of the spring is at one end. while the more flexible portion is at the other end and preferably also the graduatlon from end to end is approximately uniform.

The preferred way to accomplish this is making the convolutions of the spring taper uniformly from one end to the other. Preferably the spring is helical and preferably the convolutions are all of the same internal diameter. Preferably, the tapering is by thinning down the sides that lie adjacent each other in the completed spring. and in such case the external diameter of the spring will be uniform, as well as the internal diameter.

In order to cause the flexible portions of a torque and the spring to cease functioning as ordinary springs. progressively. as the torque load increases. the arrangement should be such of the spring can become wound up so as to transmit the torque mainly by longitudinal tension of the material of the spring. thus progressively shifting the spring function to progressively stiffer portions of the spring. There are various ways of accomplishing this, as for instance, by providing a bearing surface against which the more flexible portions of the spring can wind themselves until further spring yield is thereby prevented. lVhile such surface might be provided on the shaft or sleeve which the spring encircles. I prefer to have surfaces of adjacent convolutions of the spring itself serve this Patented Aug. 16', 1921.

function. To this end the adjacent surfaces of the spring convolutions are preferably substantially flat, and they are wide enough to afford safe bearing surfaces one against the other. With this arrangement theflexible portions perform their normal spring function until the torque stress becomes sufficient to bring adjacent surfaces of the convolutions in contact. This requires that the material of the spring be stiff in a radial direction; that the initial space between convolutions be not too great; and that the organization of parts be such as will permit an endwise shortening of the spring helix as a whole.

The above and other features of my inventionmay be more fully understoodfrom the following description in connection with the accompanying drawings in which Figure 1 is a side elevation partly in axial section showing the motor, shaft, pinion and torque mechanism in operative relation to a portion of the fly whtel ofan engine;

Fig. 2 is a diagram showin in a general way some of the characteristlcs of the or-' dinary torque spring as contrasted with those of .a spring made in accordance with my invention.

In the drawings the drive shaft 1 carries end-wise-movablesleeve 2 having threaded thereon the toothed pinion 3. Torque is. applied to pinion 3 from radial bolt 4 around which is coiled one end of spring 5, clamped by nut 6. The other end of spring 5 surrounds a hollow stud 6 on sleeve 2 and is clamped in place by screw 7. The axis of shaft 1 is parallel with the axis of the fly wheel 12 and the teeth 8 of pinion 3 are in proper relation for endwise sliding engagement with teeth 9 on said fly wheel.

The pinion 3 has the "usual eccentric weight 10, the inertia and eccentricity of which are relied upon to multiply the tendency of the pinion to stand still when the driving shaft 1' issuddenly started, and also the tendency of said pinion to overrun when the shaft 1 suddenlystops or slows down, or the fly wheel 12 speeds up. On starting, the quick-starting shaft and sleeve automatically screw the slow-startingpinion to ward engagement with gear 9 and on stopping or overrun'ning, the pinion is screwed out of engagement.

The spring 5 normally operates to hold sleeve 2 in the position shown in the drawings, in addition to transmitting thereto the torque applied through shaft 1 and bolt 4. Sleeve 2, however, is free to yield longitudinally in a direction to compress spring 5 under various conditions, as for instance, when the teeth of pinion 8 happen to butt against the ends of teeth 9, in such case the pinion not being able to screw further to the left, naturally screws the sleeve to the shaft 1 through the right, thus endwise compressing spring 5. Conversely if the twist on spring 5 becomes very great its convolutions tend to close,

thereby shortening the spring and drawing sleeve 2 to the right.

By reference to the seen that the successive convolutions 5, 5, 5", 5, 5 etc. are progressively of less cross section; also that this is accomplished-in the preferred way, that is, by thinning the mate- With the above structure for the spring,

it is obvious that the initial flexibility will be that of the thinnest convolution, 5; also that when the load gets too great for 5, the latter will become a mere tension member. As before stated, this may be accomplishedby the winding down of the convolution to smaller diameter until it contacts with sleeve 2, but preferably the proportion and arrangement of parts is such that the well known tendency of a helical spring to shorten will be availed of to bringthe face of 5 into contact with 5, whereupon the spring will have an effective resilience progressively g The proportions, particularly. the degree and rate of taper of the material shown in the drawings, is for purposes of illustration only, and it will be understood that this can be varied however,

within wide limits. Preferably, convolution 5 is heavy enough to function normally as a helical spring, underany possible strain that. can occur in prac- /tice, while convolution 5 is for easy cushioning of concussion, either on meshing or unmeshing of pinion 3 with fly wheel 12, It isto be noted that as shown in the drawings, the gap between the right hand end of the sleeve 2. and the left hand end of sleeve 11 is as great as the aggregate of all the spaces normally separating convolutions 5, 5, 5 etc. While .this may be desirable as permitting complete wind-up of all convolutions, it is not necessary, and in certain cases it will be found desirable to decrease this gap to afford a rear stopfor the sleeve before all-the convolutions have come into lateral contact.

With the spring shown, 1t may be desir-- drawings it will be equal to that of convolution-5 and so on flexible enoughsprings of uniform cross section are indicated diagrammatically in F ig. 2, in which the horizontal line aZ is an ordinate, representing increasing angles of torque as the spring is wound up under increasing load, while the vertical line a-c is the ordinate indicating the increase of spring resistance according to increase of wind-up of the spring.

llitli reference to these ordinates the common, uniform-section, helical spring of the prior art may be considered as having resistance characteristics of the type represented by the line (Z, c, 7', while springs constructed in accordance with invention have characteristics like those indicated by the curve g, k, 2'. These curves are not supposed to be quantitatively accurate, and-it is obvious that extremely wide variations, are available through selection of different materials, dimensions and designs for the respective types of springs. In all cases, however, the same general characteristics will appear.

In the case of my spring the initial resilience afforded by the spring when the torque first comes on, as represented by the vertical line a, 9, may be relatively small. The increase of spring resistances, as the spring winds up will at first be very gradual, but the increasing stiffness of the'spring as the wind-up increases, is very marked. Moreover, when a point, as say it, has been reached there may still be a reserve of stifl ness' in the last turn or two of the coil that will afford a substantial margin for spring yield even under extreme conditions of stress.

On the other hand, the cross section throughout affords a more nearly. proportional increase of stiffness from the start as (Z, to a point as e, where all the convolutions become wound up simultaneously, and further yield is practically impossible up to the breaking point of the spring of uniform spring, as is indicated by the substantially vertical direction of the line from e to f.

A further important feature is that a uniform spring, in order to have approximately the same greater initial stiffness as indicated by vertical acZ as contrasted with the initial stiffness indicated for my spring by the shorter vertical (6[/.

It will be understood that these values and rates of change of values are arbitrarily selected for purposes of illustrating in a, very general way the characteristic differences of the springs, and, in particular the very practical fact that I can have my spring resistances at starting much lower and my maximum resistances much possible with a spring in which the material is of uniform cross section.

While I have shown and described an type, stiffer at the other end higher, than is illustrative embodiment of my invention, it will be obvious that the cooperating driving and driven elements are capable of wide variation. Also that the torque spring between them may have its flexible portion and stifi'er portions associated in various ways, and arrived at by widely varying selection of materials, shapes and sizes. As for instance, the cross sectional shape of the material of the spring may be the same throughout, cross section area only being varied; or where one dimension is maintained, the maintained dimension may be longitudinally of the coil, while the diminishing dimension is radial of the coil; also, that in general the great variation of cross section indicated in the drawings will usually be unnecessary since the stiffness of 'a spring tends to decrease in a much higher ratio than the de-- crease of its cross section. In this connec tion it is to be noted that where, for any reason, it is found desirable to have the great variation indicated in the drawing. as say 4 to 1, it may be desirable to regulate the taper in such a way as to give approximately regular proportional degrees of spring strength, instead of merely decreasing the taper uniformly and allowing the strength to decrease, according to its own law which might be more nearly as a square or cube of cross section than as a direct proportion. I have found, however, that where the taper from stiff" to flexible involved decrease of cross section not greater than say 2 to 1, the taper may be perfectly uniform, with very satisfactory results.

claim 1. A starting device comprising a driving element, a rotatable element driven thereby,

a power receivin and transmitting device mounted to trave longitudinally on said rotatable element, and a yielding driving connection between said elements, comprisinga. spring-having a stiff portion and a more flexible portion for the purpose described.

2. A starting device comprising a rotatable driving element, a rotatable element driven thereby, and an intermediate powertransmitting torque spring of the helical one end and more flexible at than is required for normal functioning as a spring under conditions of ordinary use.

3. A. starting device comprising a rotatable driving element, a rotatable element driven thereby, and an'intermediate powertransmitting torque spring having the material of one portion substantially thicker than another portion.

4. A starting device comprising a rotatable driving element, a rotatable element driven thereby, and an intermediate powertransmitting torque spring of the helical type having convolutions in one portion of its length, flexible so as to afford relatively small initial resilienc another portion of th stiffer to wihstand the maximum driving torqu 5. A starting table driving driven thereby transmitting torque spri type, stiffer at one end an the other end than is require functioning as a sprin ordinary use; ments being relative tion to said spring, and longitudinally, w shorten under torque 6. A starting table driving e driven thereby, transmitting torque spring; driven elements being relat1 opposi entially and longitud spring may shorten un and .said spring being 0 substantially stiffer others, and having a lutions formed to a when the length 0 with the accompany movement of said d bers.

7. A starting device table driving element, driven thereby, and an 1 transmitting torque sprin driven elements oppositio entially and spring may sh device compri ment, a rotatable e and an mte said driving an device comprising tion to said spring,

f the spring is ing relative being relati n to said spring,

longitudinally,

orten under torque e at starting, and in and said spring being of the helical type, e length substantially substantially more flexible at one end than strains at times of at theother; the parts being proportioned e and load.

sing a rotaa more flexibleportion of thespring will lement become wound up and o erate as .a tension and arranged so that under normal full load rmediate powermember totransmit while the stiffer end of the helical continues to function as a helical spring. more flexible at 8. A starter for engines comprising in d for normal combination with a motor driven shaft, a conditions of screw-threaded sleeve mounted for rota d driven eleand longitudinal movement thereon, a yiel ly movable inopposiing driving connection between the shaft both circumferentially. and sleeve comprising a coiled spring which hereby said spring may hasone end anchored to the shaft and the other to the sleeve, and a driving pinion a rotawhich is screw-threaded upon said sleeve and lement, a rotatable element adapted to travel longitudinally thereon and an-intermediate powerwhen the shaft and its sleeve are rotated,

said driving and said spring being more flexible at one end vely movable in than at the other for the purpose described. both "circumfer- 9. A starter for engines comprisin in vwhereby said combination with a motor driven shaft, a der torque or thrust; screw-threaded sleeve mounted for rotary f the helical type and and longitudinal movement thereon, a yieldoints than at ing driving connection between the shaft and djacent sides of convosleeve comprisig a coiled spring which has iford bearing surfaces one end anchored to the shaft and the other shortened to the sleeve, and a driving pinion which is longitudinal screw-threaded upon said sleeve and adapted riving and driven memto travel longitudinally th'ereon when the shaft and its sleeve are rotated, said spring comprising a rota being more flexible at the sleeve end than at a rotatable element the shaft end and said sleeve being extended ntnermediate powerrearwardly beneath the said flexible portion. g; said driving and Signed at New York, in the county of New vely movable in .York, and State of New York this 17th day both circumferof December, A. D. 1920.

whereby said or thrust, SAMUEL W. 'RUSHMORE; 

